'GO THE CLIMATES OF THE GEOLOGICAL PAST 



During the Ordovician, Silurian and Devonian periods, 

 which followed the Cambrian, the continents became largely 

 worn down and resubmerged. This was the effect of 

 the cessation of those uplifts of continents and subsidences 

 of ocean basins that characterised the previous cycle. 

 The continents would be worn doAvn by rivers, and the 

 oceans would tend to silt up, causing the waters to rise. 



The carboniferous and early Per mo- Carboniferous, 

 which followed the Devonian, were periods of fluctuating 

 conditions, as shown b}'^ the intercalation of land and 

 swamp deposits, like coal beds, between marine sediments. 

 The late Permo- Carboniferous and Triassic were periods 

 of elevation or continental extension, and the most marked 

 result of the inequalities in level produced was that some 

 areas became cold and arid (like the Thibet and Gobi 

 to-day), and other areas became ccld and humid (like the 

 west coast of Scotland to-day). 



At the end of the Triassic, uplifts ceased, and the 

 following periods, the Cretaceous and Eocene, saw the 

 continents worn down and largely resubmerged. Absence 

 of high mountains and the prevalence of marshy conditions 

 naturally produced warm climates. 



In the middle and late Tertiary periods which followed 

 the Eocene, particularly in the Miocene and Pliocene, 

 great uplifts again took place. This resulted in the pro- 

 duction of high altitudes and cold climates. The Alps 

 and the Himalayas, and many of our highest tablelands 

 of to-day, were formed during these periods. 



It is clear that the three greatest Ice Age«, the Cam- 

 brian, the Per mo- Carboniferous, and the late Teritary, 

 correspond with periods of uplift or " continental 

 extension." 



The researches of Professors Hull and Spenser show 

 that Europe and North America stood many thousand 

 feet higher in the period of the Great Ice Age than at 

 present. The drowned valleys off the Victorian coast, 

 and the rugged coastline of south-eastern Australia, show 

 that this part of our continent was much higher when an 

 ice-age prevailed on Mount Koscuisko, the Australian Alps- 

 and in Tasmania. 



It is therefore quite possible that the Ice Ages of 

 treological history have all seen produced essentially by the 



